The invention relates to a concavely curved sliding element whose multilayer system, applied to a backing member in particular in a vacuum, comprises at least one overlay of a metallic dispersion alloy. Such sliding elements have acquired importance for example as highly loadable bearings or bearing liners in combustion engines. The invention further relates to a method of producing such sliding elements, which are also known as radial bearings.
1. Field of the Invention
2. Description of Related Art
In the case of radial bearings, the highest stress, i.e. abrasive loading, generally arises in the area of the apex of the bearing liner. In contrast, in the vicinity of the partial faces, i.e. the areas remote from the apex, wearing and dynamic loads are substantially less. Through preliminary mechanical work affecting the geometric shape, e.g. softening of the arcuate shape, it has been attempted, inter alia, to ensure the formation of an optimum lubricating film and embedding behaviour for foreign particles.
If differences in thickness between the apex area and the area of the partial faces arise during application of the multilayer system, the overlay deviates from the ideal circular shape. Through prior machining of the backing member, it is possible to compensate for this. However, this measure makes prior machining considerably more difficult and more expensive.
Bearing liners with uniform wall thicknesses may also be used for V-type engines and engines with obliquely divided connecting rods. The main load zone therein lies outside the apex area.
In the case of highly loadable sliding elements, it is known to apply the overlays by vacuum coating. Thus it is known to apply an Al--Sn--Cu--based overlay by atomisation (sputtering) (DE 28 53 724 C3; DE 29 40 376 A1; DE 37 29 414 A1).
It is also known to spray on layers with integral plastics particles (DE 29 14 618 C2).
Moreover, an atomising device specially conformed to the coating geometry of bearing liners or a device for accommodating backing members for the production of plain bearings by atomisation are known. In general, highly loadable overlays may be produced using the above-mentioned materials applied by atomisation in a vacuum (AT-PS 392 291 B; EP 0 452 647 A1). However, owing to its working mechanism, atomisation is an expensive method because the deposition rate cannot be increased above a certain limit. This method therefore has narrow limits. On the other hand, atomisation had the advantage that uniform coating is possible even on curved components such as plain bearings.
It is also known to produce plain bearings from strip-form semi-finished products, wherein an overlay is applied to the strip by vacuum vapour-deposition (DE 36 06 529 C2; DE 29 35 417). The aim of this known method was more economical production of plain bearings. However, attempts to process a strip coated in this way further to form a plain bearing did not produce a usable result, because the high degree of deformation led to damage or breakages within the multilayer composite.
The problem on which the invention is based is that of so constructing the layers of a multilayer system of a highly loadable sliding element or plain bearing that the latter fulfil the requirements made thereof under all loads arising during operation and at the same time reducing manufacturing costs. An optimum lubricating film which has a substantial influence on service life is to be produced. The method is to be environmentally friendly, i.e. electroplating methods should be superseded at least in part, and highly productive.